All of my composting books agree that pet hair is a great source of nitrogen.

The 'Bible' of composting, The Rodale Book of Composting, says: Between 6 and 7 pounds of hair contain as much nitrogen as 100 to 200 pounds of manure. Like feathers, hair will decompose rapidly in a compost pile but only if well moistened and thoroughly mixed with an aerating material. Hair tends to pack down and shed water, so chopping or turning the pile regularly will hasten decay.

Hmm... after reading that, I realise I'd better get out there tomorrow and break up the clumps of hair.